Proximodistal Exploration in Motor Learning as an Emergent Property of Optimization

International audienceTo harness the complexity of their high-dimensional bodies during sensorimotor development , infants are guided by patterns of freezing and freeing of degrees of freedom. For instance, when learning to reach, infants free the degrees of freedom in their arm proximodis-tally, i.e. from joints that are closer to the body to those that are more distant. Here, we formulate and study computationally the hypothesis that such patterns can emerge spontaneously as the result of a family of stochastic optimization processes (evolution strategies with covariance-matrix adaptation), without an innate encoding of a maturational schedule. In particular, we present simulated experiments with an arm where a computational learner progressively acquires reaching skills through adaptive exploration, and we show that a proximodistal organization appears spontaneously, which we denote PDFF (ProximoDistal Freezing and Freeing of degrees of freedom). We also compare this emergent organization between different arm morphologies – from human-like to quite unnatural ones – to study the effect of different kinematic structures on the emergence of PDFF. Research highlights. • We propose a general, domain-independent hypothesis for the developmental organization of freezing and freeing of degrees of freedom observed both in infant development and adult skill acquisition, such as proximo-distal exploration in learning to reach

Emergent Jaw Predominance in Vocal Development through Stochastic Optimization

International audienceInfant vocal babbling strongly relies on jaw oscillations , especially at the stage of canonical babbling, which underlies the syllabic structure of world languages. In this paper, we propose, model and analyze an hypothesis to explain this predominance of the jaw in early babbling. This hypothesis states that general stochastic optimization principles, when applied to learning sensorimotor control, automatically generate ordered babbling stages with a predominant exploration of jaw movements in early stages. The reason is that those movements impact the auditory effects more than other articulators. In previous computational models, such general principles were shown to selectively freeze and free degrees of freedom in a model reproducing the proximo-distal development observed in infant arm reaching. The contribution of this paper is to show how, using the same methods, we are able to explain such patterns in vocal development. We present three experiments. The two first ones show that the recruitment order of articulators emerging from stochastic optimization depends on the target sound to be achieved but that on average the jaw is largely chosen as the first recruited articulator. The third experiment analyses in more detail how the emerging recruitment order is shaped by the dynamics of the optimization process

A psychology based approach for longitudinal development in cognitive robotics.

A major challenge in robotics is the ability to learn, from novel experiences, new behavior that is useful for achieving new goals and skills. Autonomous systems must be able to learn solely through the environment, thus ruling out a priori task knowledge, tuning, extensive training, or other forms of pre-programming. Learning must also be cumulative and incremental, as complex skills are built on top of primitive skills. Additionally, it must be driven by intrinsic motivation because formative experience is gained through autonomous activity, even in the absence of extrinsic goals or tasks. This paper presents an approach to these issues through robotic implementations inspired by the learning behavior of human infants. We describe an approach to developmental learning and present results from a demonstration of longitudinal development on an iCub humanoid robot. The results cover the rapid emergence of staged behavior, the role of constraints in development, the effect of bootstrapping between stages, and the use of a schema memory of experiential fragments in learning new skills. The context is a longitudinal experiment in which the robot advanced from uncontrolled motor babbling to skilled hand/eye integrated reaching and basic manipulation of objects. This approach offers promise for further fast and effective sensory-motor learning techniques for robotic learning

Integrating reinforcement learning, equilibrium points and minimum variance to understand the development of reaching: a computational model

Despite the huge literature on reaching behaviour we still lack a clear idea about the motor control processes underlying its development in infants. This article contributes to overcome this gap by proposing a computational model based on three key hypotheses: (a) trial-anderror learning processes drive the progressive development of reaching; (b) the control of the movements based on equilibrium points allows the model to quickly find the initial approximate solution to the problem of gaining contact with the target objects; (c) the request of precision of the end-movement in the presence of muscular noise drives the progressive refinement of the reaching behaviour. The tests of the model, based on a two degrees of freedom simulated dynamical arm, show that it is capable of reproducing a large number of empirical findings, most deriving from longitudinal studies with children: the developmental trajectory of several dynamical and kinematic variables of reaching movements, the time evolution of submovements composing reaching, the progressive development of a bell-shaped speed profile, and the evolution of the management of redundant degrees of freedom. The model also produces testable predictions on several of these phenomena. Most of these empirical data have never been investigated by previous computational models and, more importantly, have never been accounted for by a unique model. In this respect, the analysis of the model functioning reveals that all these results are ultimately explained, sometimes in unexpected ways, by the same developmental trajectory emerging from the interplay of the three mentioned hypotheses: the model first quickly learns to perform coarse movements that assure a contact of the hand with the target (an achievement with great adaptive value), and then slowly refines the detailed control of the dynamical aspects of movement to increase accuracy

Two photon interrogation of hippocampal subregions CA1 and CA3 during spatial behaviour

The hippocampus is crucial for spatial navigation and episodic memory formation. Hippocampal place cells exhibit spatially selective activity within an environment and form the neural basis of a cognitive map of space which supports these mnemonic functions. Hebb’s (1949) postulate regarding the creation of cell assemblies is seen as the pre-eminent model of learning in neural systems. Investigating changes to the hippocampal representation of space during an animal’s exploration of its environment provides an opportunity to observe Hebbian learning at the population and single cell level. When exploring new environments animals form spatial memories that are updated with experience and retrieved upon re-exposure to the same environment, but how this is achieved by different subnetworks in hippocampal CA1 and CA3, and how these circuits encode distinct memories of similar objects and events remains unclear. To test these ideas, we developed an experimental strategy and detailed protocols for simultaneously recording from CA1 and CA3 populations with 2P imaging. We also developed a novel all-optical protocol to simultaneously activate and record from ensembles of CA3 neurons. We used these approaches to show that targeted activation of CA3 neurons results in an increasing excitatory amplification seen only in CA3 cells when stimulating other CA3 cells, and not in CA1, perhaps reflecting the greater number of recurrent connections in CA3. To probe hippocampal spatial representations, we titrated input to the network by morphing VR environments during spatial navigation to assess the local CA3 as well as downstream CA1 responses. To this end, we found CA1 and CA3 neural population responses behave nonlinearly, consistent with attractor dynamics associated with the two stored representations. We interpret our findings as supporting classic theories of Hebbian learning and as the beginning of uncovering the relationship between hippocampal neural circuit activity and the computations implemented by their dynamics. Establishing this relationship is paramount to demystifying the neural underpinnings of cognition

AFFORDANCES IN EARLY MOTOR DEVELOPMENT: THE ROLE OF CONTEXTUAL FACTORS

Early motor development is a complex phenomenon characterized by a high degree of inter- and intra-individual variability. The primary objective of this work was to test a conceptual model of early motor development that considers the key contextual factors relating to the home environment, infant characteristics, and caregiving practices. Given the lack of appropriate measures targeting these contextual factors, a secondary objective was to develop and run preliminary analyses of two new measures that assess these factors in relation to the motor development of infants aged 4 to 10 months of age. Following the initial item generation phases, exploratory principal components analyses with varimax rotations were run to determine a factor structure for each measure, followed by a confirmatory factor analysis. These measures were then incorporated into the larger conceptual model, which tested the extent to which these contextual factors explained the variability observed in motor developmental scores as measured by the Alberta Infant Motor Scale. Using structural equation modeling, these direct effects, as well as indirect effects mediated through the Daily Activities of Infants Scale are discussed. The measurement model demonstrated good fit indices (% = 477.9, df = 369, p \u3c 0.01; IFI; 0.940; TLI 0.927; CFI 0.938; RMSEA 0.04) indicating the model fits the data. Analysis of path coefficients revealed that the contextual factors did not explain a significant portion of the variance in early motor development (32%). The factor Opportunities in the Playspace was found to explain 24% of the variance in scores and was significant. Although the results of this work do not provide strong evidence for a role of contextual factors in motor development, they do raise questions about the use of linear statistical analyses to measure non-linear processes and the developmental variations of infants bom full-term and those bom preterm. Full-term infants are known to be resilient and it is suggested that the subtle determinants, such as those concerning contextual factors, might play a more important role in a population of infants who are vulnerable or considered to be at risk

Insular adaptations in the appendicular skeleton of Sicilian and Maltese dwarf elephants

This thesis investigates the evolution of Pleistocene insular proboscideans from the centralwestern Mediterranean (Palaeoloxodon species from Sicily, Malta, Favignana) and a mammoth (Mammuthus lamarmorai) from Sardinia, with a particular emphasis on the anatomy of the limbs. Differences in the morphology of the limbs are examined across a tenfold reduction in mass (from 3,5m-tall P. antiquus from Germany to 1,2 m-tall P. ex gr. P. falconeri from Spinagallo Cave, Sicily), revealing insights into significant morphological changes in the long and foot-bones, particularly appendicular changes evident in SiculoMaltese P. ex gr. P. falconeri. Notable morphological differences between P. antiquus and its insular descendent P. ex gr. P. falconeri include the functional morphology of the ankle-joint (especially the calcaneus' articular facet for the tibia). Furthermore, morphological similarities found between the femur of young continental elephants (P. antiquus and L. africana) and adult insular dwarfs (P. ex gr. P. falconeri and its probable ancestor Palaeoloxodon sp. from Lparello Fissure, Sicily) suggest evidence of paedomorphism in the limbs. Similarly, comparisons of the ontogenetic allometry of the tibia in L. africana and P. ex gr. P. falconceri include changes which are also consistent with paedomorphism, although other factors could not be ruled out. In the humerus large differences are evident in the morphology of the deltoid tubercule between co-generic insular Palaeoloxodon species, suggesting interspecific differences in the musculo-skeletal system. Furthermore, on the basis of dimensions, morphology and stratigraphy, the large Palaeoloxodon sp. remains from Luparello Fissure, north-western Sicily are suggested to belong to the ancestral chronospecies of P. ex gr. P. falconeri from Sicily, which may have subsequently colonized Malta during the reduced sea-levels of a Middle Pleistocene glacial lowstand (following a corridor with reduced distances between the two islands). Additionally, morphological differences in the calcanei of elephants from Luparello Fissure, Sicily, and Benghisa Gap, Malta may be the result of allopatric speciation between similar-sized elephants during the Middle Pleistocene, or alternatively relate to ecomorphology. These findings suggest that the morphology of the calcaneus may be more informative than hitherto recognised for resolving systematics and taxonomy among the Elephantini. Furthermore, although the absolute chronology of SiculoMaltese elephants remains poorly constrained, preliminary U-Th dating at Alcamo Quarry, western Sicily suggests a tentative early Middle Pleistocene age for Palaeoloxodon sp

Palynofacies and sedimentology of some Late Jurassic sediments from the British Isles and northern North Sea

The variation of physical, chemical and ecological conditions through stratified water bodies is shown to be a useful integrating tool in the palaeoenvironmental modelling of epeiric sea facies. Particular emphasis is placed on the implications of oxygen deficiency in meromictic water bodies for the deposition of 'black shales'. In epeiric settings preservation is probably a more important determinant of black shale deposition than primary productivity. Optimal preservation of marine carbon occurs in dysaerobic to anoxic bottom waters. Such facies can be identified by a synthesis of sedimentological, geochemical and palaeoecological data. In dysaerobic to anoxic environments the kerogen is dominated by amorphous material of marine, but indeterminate, origin. The proportion of terrestial organic matter correlates with grain size, proximity to fluvial sources and level of oxygenation. Palynomorph assemblages vary along gradients of hydrodynamic energy and proximity to fluvial sources. Dinocysts can be directly related to hydrographic stability; they are rare in basinal, bottom water, sediments except when redeposited. The Oxfordian Piper Formation was deposited in an aerobic, hydrographically unstable, shallow shelf regime. palynofacies trends suggest an approximately NW-SE onshore-offshore gradient. Apart from scale the Piper sequence is analogous to coeval onshore sediments at Brora. The eudoxus-pectinatus zones of the Type Kimmeridge Clay were deposited in a distal basin with an alternating mixed (aerobic-dysaerobic) and meromictic (dysaerobic-anoxic) watermass. The resulting cyclicity is analagous to Quaternary sapropel sequences. Coccolith limestone intercalations are interpreted as indicative of partial mixing of a meromictic watermass. A formal subdivision of the Type Kimmeridge Clay Formation is proposed. Kimmeridgian sediments of the Brora-Helmsdale outlier comprise dysaerobicanoxic basinal shales with interbedded redeposited sandstones. A similar, but more proximal, facies association is observed in the Toni-Thelma area. Late Jurassic distal, basinal, dysaerobic-anoxic shales occur in the Maureen field

The development of coordination for reaching movement in children

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal